1. Technical Field
This disclosure relates generally to a power transmission apparatus designed to transmit power, as produced by an internal combustion engine, to auxiliary devices.
2. Background Art
There are known power transmission systems which work to transmit output power of an internal combustion engine to a given accessory and other accessories mounted in, for example, an automobile using an endless transmitting member such as a belt. The given accessory is used as, for instance, an engine starter to start the internal combustion engine. The given accessory may be rotated by the output power of the internal combustion engine along with the other accessories in a regenerative mode of operation to generate electricity. Japanese Patent First Publication No. 2006-299844 teaches the above type of power transmission system which has an auto-tensioner disposed between a driving pulley and a pulley of one of the accessories (which will also be referred to as an accessory pulley below) to adjust the degree of tension of the endless transmitting member to a required level.
The auto-tensioner of the power transmission system, as taught in the above publication, is equipped with a tensioner pulley, a tensioner body, a biasing mechanism, and a stroke inhibitor. The tensioner pulley is placed in contact with the endless transmitting member between the driving pulley and the accessory pulley and movable relative to the internal combustion engine. The tensioner body is capable of contracting or extending in a given direction to move the tensioner pulley relative to the engine. The biasing mechanism urges the tensioner body to extend at all times. The stroke inhibitor serves to hold the tensioner body from contracting.
The auto-tensioner works to extend or contract the tensioner body to move the tensioner pulley relative to the engine, thereby regulating a degree of tension of the endless transmitting member. Specifically, the auto-tensioner is capable of eliminating the loosening of the endless transmitting member between the driving pulley and the accessory pulley when the given accessory operates in a regenerative mode. When the given accessory operates in a power mode, it will result in an increase in tension of the endless transmitting member between the driving pulley and the accessory pulley, which moves the tensioner pulley to a given position. When the tensioner pulley reaches the given position, the torque, as produced by the given accessory, is transmitted through the endless transmitting member to a drive shaft of the internal combustion engine to crank the internal combustion engine.
The power transmission system is designed to sequentially execute a reverse rotation control step, a stroke inhibition step, and an engine start step. When or after an engine stop condition is met, the reverse rotation control step is executed to rotate the given accessory in the reverse direction to loosen the endless transmitting member between the driving pulley and the accessory pulley, thereby causing the tensioner body to extend in the given direction. The stroke inhibition step is to control the operation of the stroke inhibitor to hold the tensioner body from contracting. The engine start step is to operate the given accessory in the power mode to crank the internal combustion engine. Specifically, the power transmission system works to extend the tensioner body to increase the degree of tension of the endless transmitting member in the reverse rotation control step and then hold the tensioner body from contracting in the stroke inhibition step, thereby keeping the tension of the endless transmitting member at an increased degree to eliminate slippage of the endless transmitting member on each of the pulleys when it is required to operate the given accessory in the power mode to start the internal combustion engine.
The power transmission system is, however, required to finely control the operation of the given accessory to output a degree of torque within a range which is higher than that permitting the tensioner body to extend in the given direction and is lower than that causing the drive shaft to start rotating in the reverse direction. When the above torque range is narrow, it results in a difficulty in keeping the output, as produced by the given accessory, within the torque range at all times.
When the torque, as produced by the given accessory which reverses in the reverse rotation control step, is lower than that causing the tensioner body to extend in the given direction, it will result in a difficulty in increasing the tension of the endless transmitting member to a required degree, which may lead to the slippage of the endless transmitting member on each of the pulleys. Alternatively, when the torque, as produced by the given accessory which reverses in the reverse rotation control step, is greater than that causing the drive shaft to be reversed, it will cause the internal combustion engine to be reversed.